Parallel Hydraulic Hybrid Vehicles are being used in many places around the world & these vehicles use alot less fuel than regular vehicles.
Hydraulic hybrid vehicles, or HHVs, like all hybrid vehicles, use two sources of power to drive the wheels. In a hydraulic hybrid, pressurized fluid is used, instead of electric power as in electric hybrids, as the additional or alternative power source along with a conventional internal combustion engine (ICE) propulsion. The presence of the hydraulic powertrain is intended to achieve better fuel economy than a conventional vehicle.
The main difference between hydraulic hybrids and electric hybrids is that hydraulic hybrids recover a vehicle's kinetic energy during braking and decelerating significantly more efficiently than electric systems; hydraulic hybrids are able to capture and reuse 70%-80% of the vehicle's braking energy compared to 25% for electric hybrids. For trucks and buses, hydraulic systems can also be less expensive than electric systems